Huntington's Disease is an autosomal dominant neurologic disorder characterized by chorea, eye movement abnormalities, and dementia. Significant weight loss is a common finding early in the course of the disease despite reportedly normal or increased caloric intakes indicating a possible increase in energy expenditure. We hypothesize that energy expenditure is increased in patients with Huntington's Disease as a consequence of the movement disorder. To test this, basal metabolic rate, 24-hour energy expenditure, and non-resting energy expenditure (all measured using the human respiratory chamber on the Research Ward of the Clinical Diabetes and Nutrition Section), and 7-day free-living energy expenditure (measured using the doubly-labeled water technique) will be compared in three groups of patients with Huntington's Disease with varying degrees of chorea (asymptomatic, mild, and moderate) to age-, sex- and weight-matched controls. To correct energy expenditure for differences in metabolically active (primarily lean) body mass among subjects, all individuals will have body composition measured by anthropometry, bioelectrical impedance analysis, and dual energy x-ray absorptiometry scanning. A total of 24 subjects (12 patients and 12 controls) have been studied to date. Twenty-four energy expenditure measured in the respiratory chamber was significantly higher in patients than controls (2109+/-97 vs. 1788+/-88 kCal/24h, p<0.05). Free living energy expenditure measured by doubly-labeled water was also higher in patients than controls (2410+/-121 vs. 2169+/- 116 kcal/24h) although this difference was not statistically significant. Basal metabolic rate was not higher, in contrast, suggesting that increased energy expenditure among patients with Huntington's Disease is attributable to the movement disorder. To test this, additional subjects who are known to be carriers of the genetic mutation, but who have not yet manifested symptoms will be compared to normal controls. These studies should help distinguish increases in metabolic rate directly attributable to the gene defect from those secondary to the movement disorder. In addition to providing insight into the pathophysiologic abnormalities in Huntington's Disease, the results may improve the care of patients with Huntington's Disease and other persons with movement disorders by providing more precise estimates of their caloric needs.